The invention relates to a blade and a rotor for a gas turbine and to a method of joining blade parts of a gas turbine, a blade-body section and at least one further blade part being provided.
Blades for gas turbines essentially comprise a blade body and a blade root, with which the blade is fastened to a rotor or stator. For fluidic control, the blades, i.e. both the guide blades and the moving blades, may have inner and/or outer shroud bands. In this case, it may be necessary, for reasons of strength, to make the blade body and the blade root or the shroud bands from different materials and to therefore first of all provide them individually and to then join them to one another. The latter applies even if the blade body is made, for example, of TiAl by powder metallurgy and cannot be cast or forged for producing the finished blade.
U.S. Pat. No. 3,768,147 discloses a method of producing a blade from a cast blade-body blank and a forged blade root, in which method the blade-body blank has a root considerably enlarged over its cross-sectional area and a likewise enlarged joining section having a joining area, at which a joining area of a blade base is positioned in alignment, the blade-body blank and the blade base being welded to one another by means of friction welding, and then the blade body being produced from the blade-body blank and the blade root being produced from the blade base, for example by machining. In this case, it proves to be a disadvantage that both the blade body and the blade root have to be provided as a blank in order to provide the joining areas required for the friction welding. In addition to considerable consumption of material, this leads to expensive and time-consuming reworking consisting of many production steps. In addition, a considerable bead occurs in the joining area during the welding, which bead likewise has to be removed.
The problem of the invention is to join individual blade parts, as far as possible in their finished form, to make an integral blade or a rotor in as simple a manner as possible from the production point of view, i.e. without a large number of additional machining steps, and to provide a method for this.
According to the invention, the solution to the problem concerning the joining of blade parts is characterized in that a blade-body section is provided with at least one end joining area and the further blade part or if need be a plurality of further parts are provided with an end joining area, an inductor is arranged so as to be adjacent to the joining areas of the blade-body section and of the second blade part, the joining areas of the blade-body section and of the second blade part are positioned essentially in alignment with and at a distance from one another, and the blade-body section and the further blade part are welded to one another by energizing the inductor with a high-frequency current and by bringing them together with their joining areas touching one another.
An advantage of the method according to the invention consists in the fact that the induced, highfrequency current is concentrated in the opposite joining areas and the latter, due to the heating, become pasty or molten only in the region close to the surface, so that the blade-body section and the further blade part are pressed against one another only with a comparatively low force and over an extremely short period. For this reason, the method may also be applied to especially thin-walled, mechanically sensitive or hollow blade-body sections.
In a preferred refinement of the method, the inductor is arranged around the circumference of the joining seam, i.e. around the circumference of the joining areas of the blade-body section and of the further blade part, in which case the inductor can be arranged at a greater distance from the joining seam in the region of the blade leading edge and the blade trailing edge than in the centre region of the blade to influence heating.
At least the blade-body section and/or the further blade part is preferably held in a frictional manner during the positioning, which on account of the comparatively low pressure forces can also be readily effected in the region of the blade body.
Depending on the application, it may alternatively be expedient to hold at least the blade-body section and/or the further blade part in a positive-locking manner during the positioning, e.g. in a plastic block or the like.
In a refinement of the method, a blade root with a second blade-body section having the end joining area is provided as further blade part, it being possible for the blade root to have, for example, a dovetail or a pin or a hook for the detachable fastening to a rotor or stator.
In a further refinement, a shroud band with a second blade-body section having the end joining area is provided as further blade part, and in a further alternative exemplary embodiment a first joining area of the blade-body section is welded to a blade root having a second blade-body section and the end joining area, and an opposite, second end joining area of the blade-body section is welded to a shroud-band section having a second blade-body section and the end joining area.
In an alternative exemplary embodiment, a rotor carrier to be bladed in an integral manner is provided as second blade part, on the circumferential surface of which rotor carrier a plurality of projecting stub sections having in each case the end joining areas are formed, in order thus to provide a rotor bladed in an integral manner.
According to the invention, the solution to the problem concerning the blades is characterized in that the blade-body section and the further blade part, at their joining areas provided in each case at the end face, are welded to one another by induction welding with a high-frequency current.
The advantage of such a blade consists in its cost-effective production, since the individual blade parts can be joined to one another in their finished form without complicated reworking steps. In addition, the structure at the joint has a high strength.
In a preferred refinement, the blade is a moving blade and the further blade part is a blade root with a second blade-body section having the end joining area.
According to the invention, the solution to the problem concerning the rotor is characterized in that the blade-body sections and the stub sections, at their joining areas provided in each case at the end face, are welded to one another by induction welding with a high-frequency current.
Here too, in particular on account of the comparatively large rotor carrier, e.g. designed as a disc or ring, it proves to be advantageous that the blade parts to be joined are already present in their finished form, the welding operation can be carried out relatively quickly, and no complicated reworking steps are necessary.
Further refinements of the invention are described in the subclaims.